Material of the day: LigamentsBy: mario Camilo

Today's Material of the day is ligament. Ligaments are present in every joint of the human body. Whenever two bones meet there will be a ligament in oder to define range of motion, protect joints and bones and maintain proper structure of the body. Ligaments are extremely important to the human body because by limiting range of motion and protecting, they help maintain stability of the body. Ligament ruptures are very common in athletes and completely compromise the structure of the joint.

Pictures taken during my ACL surgery, which shows new ligament

Pictures taken during my ACL surgery, which show torn ligament.

In 2012 was the first time I realised the true importance of ligaments. While playing soccer for my high school I sprained my right foot and partially ruptured three ligaments. Stability and movement on my foot where damaged forever even after years of physical therapy. In September 2016, while playing soccer, I had my second ligament injury; however, this time was in the knee. My ACL was completely ruptured and the only way I could come back to ever playing sports again was by doing a replacement surgery. Part of my patellar tendon was removed in order to replace my broken ligament. Without the ligament instability was present and pain was recurring.

What are ligaments made of?

The main component of ligaments is collagen, constituting about 70-80% of its weight and its physical behaviour can be predicted from this material. Ligaments have a much longer turnover than bones; therefore, it takes much more time for it to recover from injury or to change structure. Ligaments and tendons are both fiber collagen connective tissues; however tendons connect muscles to bone allowing bone movement and ligaments connect bone to bone maintain control and stability of bones.

The most important structure for the ligament is the mechanical structure. In order to maintain stability and limit motion ligaments are supposed to support a lot of stress and force. In addition, when contact sports (ex. soccer, football, basketball) are being played, ligaments, specially those in the knee, face extreme forces and stresses which it must support. Ligaments completely fail after 1730 Newtons or with stresses of over 60MPa. Ligaments also have a tendency to fail when movements are opposed to the joints range of motion.

Graphs show ligaments failure and rupture after force and stress.

Ligaments are composite, anisotropic structures with Young's modulus for ligaments ranging from 1.2-1.8Gpa and ultimate stress at failure ranging from 50-150 MPa. There is a large range for both properties because various factors such as the amount of water and difficulty acquiring live human or animal information. Peak loads in ligaments are decreased with each cycle of cyclic loading and unloading, indicating ligament softness. Overuse is one of te reasons that ligaments tend to rupture, ligaments will become softer after excessive use; However, material properties will come back to normal after interrupted periods of activity.